A homogeneous mixture is a mixture having a uniform composition throughout the mixture. For example: salt in water, sugar in water, copper sulphate in water
A heterogeneous mixture is a mixture having a non-uniform composition throughout the mixture. For example: sodium chloride and iron fillings, salt and sulphur, oil and water

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(a) Saturated Solution: A solution in which no more of the solid (solute) can be dissolved at a given temperature is called a saturated solution. Suppose 50 gm of a solute is the maximum amount that can be dissolved in 100 gm water at 298 K. Then 150 gm of solution so obtained is the saturated solution at 298 K.
(b) Pure Substance: A pure substance consists of a single of matter or particles and cannot be separated into other kind of matter by any physical process. Pure substances always have the same colour, taste and texture at a given temperature and pressure. For example, pure water is always colourless, odorless and tasteless and boils at 373 K at normal atmospheric pressure.
(c) Colloid: Colloids are heterogeneous mixtures the particle size is too small to be seen with a naked eye, but it is big enough to scatter light. The particles are called the dispersed phase and the medium in which they are distributed is called the dispersion medium. Colloids are useful in industry and daily life. A colloid has the following characteristics:
• It is a heterogeneous mixture.
• The size of particles of a colloid lies between 1 – 100 nm and cannot be seen by naked eyes.
• The particles of colloid can scatter a beam of light passing through it and make the path visible.
• The particles of colloid cannot be separated from the mixture by filtration. The process of separation of colloidal particles is known as ‘centrifugation’.
• They do not settle down when left undisturbed. In other words colloids are quite stable e.g. smoke, milk, fog, cloud etc.
(d) Suspension: A ‘suspension’ is a heterogeneous mixture in which the solute particles do not dissolve but remain suspended throughout the bulk of the medium. A suspension has the following characteristics:
• It is a heterogeneous mixture.
• The size of particles of a suspension is greater than 100 nm and is visible to naked eyes.
• The particles of suspension can scatter a beam of light passing through it.
• The particles of a suspension settle down when left undisturbed.
• The particles of a suspension can be separated from its mixture by filtration.